ZN-P ALLOY ELECTROPLATED STEEL SHEET HAVING EXCELLENT CORROSION RESISTANCE

摘要

PURPOSE:To provide a titled plated steel sheet having excellent bare corrosion resistance, phosphatability, etc. by subjecting at least one surface of said sheet to electroplating of a Zn-P alloy consisting basically of Zn contg. a small amt. of P and contg. the balance of at least =1 among Ni, Co, Fe and Cr. CONSTITUTION:A Zn plating bath formed by adding a small amt. of P supply source such as sodium hypophosphite to a Zn plating bath consisting of a sulfate bath, chloride bath, fluoride bath or the mixed bath thereof, and adding further =1 kind among Ni, Co, Fe and Cr ions is prepd. For example, a cold-rolled steel sheet is dipped in the Zn plating bath and with the steel sheet as cathode, the Zn plating bath is electrolyzed by which the Zn-P alloy plating layer deposited effectively with P is formed on the steel sheet. The plating layer in this case consists basically of 70-94.5wt% content of Zn and 0.0003-0.5wt% content of P and contains the balance =1 kind among Ni, Co, Fe and Cr.